Peak demand meter



- s Shets- Sheet 1 Inventor:

h .c R. A e) m d Z my W a n P o w. A s H A 1944- I T. A. RICH 2,356,616

( PEAKVDEMAND METER Filed July 15, 1942 5 Shets-Sheet 2 $5 Inventor:

TheodoreA.T-?ich,

X His Attorney Aug 22, 1944- 6 T. A. RICH I 2,356,616

PEAK DEMAND METER Filed July 15, 1942 5 Sheets-Sheet 5.

Fig.4.

Ifiventorw Theodore AFQich,

b vVw- M y His Attorney Patented Aug. 22, 1944 UNITED PEAK DEMAND METERTheodore A. Rich, Schenectady, N. Y., assignor to General ElectricCompany, a corporation of New York Application July 15, 1942, Serial450,976

8 Claims.

My invention relates to peak demand meters and concerns improvements inthe general type of peak demand meter described in U. S. Patent2,172,176 to George F. Gardner and myself. In particular the purpose ofthe present invention is a peak demand meter of high sensitivity andaccuracy which is positive in operation and is largely immune tovibrations.

The features of my invention which are believed to be novel andpatentable will be pointed out in the claims appended hereto. For abetter understanding of my invention reference is made in the followingdescription to the accompanying drawings in Which Fig. 1 represents anexploded perspective view of my improved meter; Fig. 2 represents a sideView partially in section of a commercial form of the meter; Fig, 3shows the escapement as viewed from the rear in Fig. 1; Fig. 3a shows arear view of the escapement in a diilerent position; Fig. 4 shows thewiring diagram and Fig. 5 shows a preferred form of scale.

Referring now to Figs. 1 and 4, I represents a power circuit which issubject to heavy current loads of short duration such for example asoccur in a welding circuit. The purpose of the meter is to measure thepeak demand of such loads with high accuracy.

An important part of the meter is an electromagnet having a back yokeII, three legs I2, I3 and I4, an armature I pivoted at I6 to the openend of the center leg I3. These electromagnet parts are of course madeof magnetic material. The electromagnet has on its central leg I3 a coilI! which is energized by or in proportion to the current flowing in lineI0 and is shown connected across the secondary of a current transformerI8. Also on the central leg of the electromagnet is a coil I 9 shownbeneath coil I I. Coil I9 is a secondary or shading coil for primarycoil I! and is connected across a resistance and contacts 2| and 22 andis completely short circuited when these contacts close. The two outerlegs I2 and I4 of the electromagnet are provided with energizing coils23 and 24 connected in series across line I0 or other suitable voltagesource through a condenser 25. This connection is partially through themetal framework and structure of the meter. Thus, the connection fromcoil 24 to condenser 25 may be through the metal framework representedby a ground connection shown at 26, a metal escapement wheel 40, one ofthe contact buttons 53 thereon and contact member 22. When the armatureI5 is in the open or detracted position shown in Figs. 1 and 4, thecoils 23 and 24 are short circuited through a stationary contact 28 anda contact 29 on the armature. This short circuit path includes agrounded connection through the metal armature I5 and its pivotsrepresented by ground connection 26 and 26a. Condenser 25 preventsexcessive current flow through such short circuited connection whencontacts 28 and 29 are closed. The purpose of this arrangement is sothat current coil II, when suiliciently energized, will start movementof armature I5 to attracted position. This increases the contactresistance between contacts 28 and 29, allowing some current to fiowthrough voltage coils 23 and 24 which increases the pull on the armaturecompletely separating contacts 28 and 29, thereby fully energizing coils23 and 24, which then complete the pulling-in operation of the armaturevigorously and with suflioient force to supply the necessary operatingforce for the operation of the meter as will be explained. Hence,current coil II, when sufliciently energized, merely starts initialmovement of the armature towards attracted position and coils 23 and 24furnish the energy for the major actual pull-in operation of thearmature and the operations which it performs when attracted.

It will be noted that the pole piece at the upper end of leg I2 is belowand the pole piece at the upper end of leg I4 is above the armature sothat the magnetic pull at these points is such as to turn the armaturein the same direction, namely counterclockwise. The coils 23 and 24 areconnected to produce flux in the same direction about the magneticcircuit formed by yoke II, legs I2 and I4 and armature I5. It will benoted that the magnetic gap between the armature and the upper end ofthe central leg I3 is formed by magnetic pole piece parts 30 and 3|equally spaced from and above and below the armature at its pivot point.This double gap arrangement is important for two reasons. Its reluctanceremains substantially constant for all rotative positions of thearmature and the armature pivot friction does not change due todifferent flux values or armature positions. No armature operatingmagnetic pull occurs at such pivot gap. However, the flux crossing suchgap is available at the gaps at the extremities of the armature toproduce the initial magnetic pull which starts separation of contacts 28and 29.

The armature I5 has a connection 32 for controlling an escapement,device and a connection 33 to a spring 34 that is progressively tensioned by operation of the escapement device on the occurrence ofprogressively higher peak demands.

The power for tensionim spring 34 and operating the escapement devicecomes from a spring 3-5. the inner end of which is secured to a shaft 35to which the inner end of spring 34 is also secured. Also, on shaft 35is the pointer 31 of the meter and spring 35 is wound manually when thepointer 31 is set counterclockwise to the zero end of its scale 53.Preferably an adjustable coupling 33 is provided between springs 35 and34 for the purpose of adjusting the initial tension of spring 34 and forcalibration purposes.

The escapement wheel 40 is geared to shaft 36 through gears 4|, 42, 43and 44 such that the escapement wheel rotates at much higher speed thanshaft 36. Gear 42 is loose on its shaft 45 but has a one way drivingconnection therewith through a disk 46 secured to shaft 45, a pawl 41pivoted to disk 45 and a ratchet wheel 48 secured to gear 42. Thispermits the winding of spring 35 without operation of the escapementmechanism but requires the spring 35 to be unwound under control of theescapement.

Extending to the rear of escapement wheel 45, as shown in Fig. l, arefour pins I, 2, 3 and 4, which cooperate with two forwardly extendingstops 5 and 6 on an escapement lever I which is pivoted at 8. Fig. 3,which shows the relation of these parts as viewed from the rear of Fig.1, will assist in an understanding of their operation. When the armaturel5 and the attached escapement control finger 32 are up, the relation ofthe escapement parts are as shown in Fig. 3. At this time the operatingend of finger 32 is spaced slightly above lever I such that armature I5and 32 in moving to the energized position do not encounter anyresistance from the escapement lever 1 until the armature has gainedmomentum and is subject to the attractive force of fully energized coils23 and 24. Hence, the downward movement of finger 32 against lever 1 ispositive and forceful and moves the lever downward to the position shownin Fig. 3a against a stop 5 The upper position of lever l is determinedby a stop 5| and these steps are adjustable. Lever i is biased to itsupper position by a spring 52.

As indicated in Fig. 3, I prefer to make lever in two parts by pivotinga small inertia part 54 to lever l at 55 and interpose such part 54between the lever I and finger 32. Spring 52 and stop 5| also act on thepivoted part 54 rather than directly on lever 1. During a ratchetingoperation when finger 32 moves downward, part 54 and 1 move downwardtogether. However, when these parts move upward small inertia part 54moves upward ahead of lever I as indicated in dotted lines in Fig. 3auntil part 54 is stopped by stop 5! followed more slowly by heavierlever i. Spring 52 thus serves to assist the quick return of finger 32and the armature 15 to which it is attached, whereby the armaturecontacts at 2B and 29 are closed before the ratchet wheel 43 hascompleted its one-quarter revolution advance hereinafter described. Whenpart 54 strikes stop 52 lever action helps to pull arm 7 upward.

Escape wheel 40 is urged to turn in a counterclockwise direction asviewed from the rear in Fig. 3 by the spring 35. When lever l is up thelowermost pin l projecting from the rear of the escapement wheel 40rests against stop 5. When the lever l is forced downward, Fig. 3a, stop5 releases pin 1 and allows it to advance until it strikes stop 5 whichis lowered to engaging position with lever I as indicated. When thelever i is again raised, pin I is released by stop 6 and moves to theposition of pin 2, while pin 4 moves to the lowermost position againststop 5. Thus, each time the lever 1 is lowered and raised, wheel 40advances one-quarter revolution.

To the front of escapement wheel 40 project four contact buttons 53which cooperate with resilient contact member 22. When armature I5 is indetracted position and escapement wheel 43 is stopped by stop 5, one ofthe contact buttons 53 engages contact member 22 and moves it forwardaway from the Wheel slightly and also from engagement with contactmember 2%. Hence under this condition resistance is included in thecircuit of shading coil l9 and the grounded side of voltage coil 24 isconnected through wheel 40, one of the contact buttons 53, contactmember 22 and condenser to the line. Resistance 23 is relatively highand is included to improve the response of the instrument as will behereinafter described. The voltage coils 23 and 24 are short circuitedthrough contacts 28 and 29 until they start to separate. When sufficientline current flows in coil IT to start separation of contacts 28 and 29,current starts to flow in coils and 24 to completely separate thecontacts 28 and 29 and operate the armature to attracted position.Immediately thereafter escapement wheel advances to the positionindicated in Fig. 3a and the contact button 53 moves from under contactmember 22 and opens the circuit of voltage coils 23 and 24 and closesthe short circuit across resistance 23 at contacts 2! and 22. The fluxproduced by current coil IT in the central leg l3 of the electromagnetcollapses due to the short circuit of secondary coil I9 and also theflux produced by voltage coils 23 and 24 ceases. Hence armature l5returns to detracted position followed by the lifting of lever l andwheel 46 advances to again close the energizing connection for coils 23and 24 and remove the short circuit of secondary coil l9 betweencontacts 2! and 22 but not until after contacts 28 and 29 have closed toshort circuit coils 23 and 24. This action is repeated so long as theflux produced by current coil H is sufficient to start separation ofcontacts 28 and 29.

However, at each one-quarter revolution advance of escapement wheel 40,pointer 31 is moved upscale and spring 34 is tensioned by a proportionalamount. The tensioning of spring 34 is applied to the armature 15through extension 33 in such a direction as to oppose attraction of thearmature and hence it requires a progressively greater current in coill! to start separation of contacts 28 and 29 after each escapement andspring tensioning operation.

It will be noted that the entire assembly thus far described is pivotedon a horizontal axis at pivots at 56 and 51. This axis is parallel withand preferably coaxial with the axis of rotation of armature I5. Thatis, straps 58 and 59 support the framework 60 on which all of the partsthus far described are carried such that the framework 60 can rock orpivot about a horizontal axis through pivots and 51. The framework andparts carried thereby are balanced by weight 63 with the center ofgravity below the pivots so that it normally rests in the horizontalposition shown. Cushioning bumpers at El and 52 slightl below the frame63 prevent any large turning movement of the framework about suchpivoted axis. The purpose of this arrangement is to make the operationof the apparatus, particularly the initial movement of armature l5,immune from vibration.

'As a result of the various expedients described, the initial movementof armature I is extremely sensitive and accurately responsive to therelation between the maximum current flow in line It! and thecountertorque of spring 34 over the entire scal range of operation ofthe peak demand meter regardless of the duration of the current peaks,

The magnitude of the peak current flow in coil ii and the resulting fluxmerely controls and is not depended upon to do the operating work of themeter. In fact, a complete ratcheting advance of escapement wheel 40 maytake a very considerably longer period of time than the duration of thepeak current which initiates such operation. All that is required of thepeak current flux is to move armature l5 enough to increase the contactresistance between contacts 28 and 29. Such movement is too small to bevisible but if it occurs, current flows through operating coils 23 and24, thereby completing the separation of the contacts which increasesthe operating current through coils 23 and 24 and supplies the operatingenergy to pull armature IE to attracted position with considerableforce. I'he initial current peak may last only for a fraction of a cycleand may cease before contacts 28 and 29 are fully separated withoutfailure of the voltage flux to complete the operation. At the same time,if the peak current flux is not sufcient to overcome the pull of spring34 it will not start separation of contacts 28 and 29 even though th eakcurrent may last several cycles.

It was found that without the resistance 20 an impulse of one cycleduration required about 5% greater current to start movement of armaturei5 than an impulse of greater length. This difference was greatest atone cycle and became less until at cycles and above no difference wasnoted. Shunting resistance across the secondary shorting coil l9corrected this error so that the peak operating current through coil l!is new independent of the number of cycles duration of such peak.Condenser which is in series with the operating coils tunes the circuitand also permits of short circuiting such operating coils withoutdrawing excessive current. Low inertia part 5 5 of the escapement leverl assures that the operating coils will be short circuited at contacts2829 before such coils are connected across the line through condenser25 at the end of an escapement wheel advancing operation. The pivotedarrangement of the mechanism prevents vibrations from inadvertentlyvarying the contact resistance at contacts 28-29. The spacing of thepivot of armature [5 between pole pieces and 3| reduces friction at suchpivot. All of these factors contribute to the sensitivity and highaccuracy of the device for the purpose for which intended.

Hence while the meter is for the same purpose and performs in a mannergenerally similar to that of the meter of Patent 2,172,176, it has avery much higher accuracy and sensitivity due to the various improvementfeatures described,

As shown in Fig. 2, the commercial form of the improved meter can bemade sufficiently compact as to be enclosed in a standard form of singlephase watthour meter casing 63 having a glass cover 64 and I may use ausual form of manual resetting device 65 extending through the frontglass cover of the meter with facilities 66 for sealing the operatingcrank 61 thereof against unauthorized use.

The meter is reset in the usual Way by unsealing crank 61, pullin it outof the slot in the sealing part 66 and rotating it with arm in acounterclockwise direction to move pointer 31 down scale to the desiredposition. Crank arm 65 is then moved to the out-of-the-way positionshown and sealed in such position. Moving pointer 31 down scale windsspring 35 and unwinds spring 34. The scale length for the meter may beof the order of 300 degrees without any difiiculty as indicated in Fig.5.

For calibration purposes the initial tension of spring 34 may beadjusted by coupling 39. Contact 28 is preferably adjustable as are alsostops 5%] and 5| and spring tension 52.

The device is preferably so calibrated that the pointer 31 will move upscale a short distance from the zero stop 68, Fig. 5, with only thevoltage operating circuit energized until the tension of spring 34 isincreased to a value to hold contacts 28 and 29 closed when no currentflows in coil IT. This pointer position may be considered the zeroposition of the scale. If, now, a low value, steady state current flowsin coil H, the device will operate to move pointer 31 further up scaleuntil the tension of spring 34 again holds contacts 28 and 29 closed.Subsequent higher current surges through initialing coil I! will causemovement of the pointer further up scale, etc, such that it indicatesthe maximum surge current value which has occurred since the pointer waslast reset. The device will respond to either surges or steady statecurrent values With equal facility and accuracy, but of course a surgecorresponding to a value considerably higher than that indicated whichis of such short duration that it does not allow the mechanism timeenough for repeated operations up to the corresponding value of thesurge will not be fully recorded but this is considered to be anadvantage rather than a disadvantage because it is not desirable tounduly penalize a customer for a very occasional high surge of momentaryduration. Of course, if such a surge is repeated several times during ameter reading period, it will eventually be fully recorded,

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A peak current demand meter comprisin an electromagnet, an armaturetherefor, a first spring for biasing said armature to detractedposition, a current coil on the electro-magnet energized in accordancewith the variable load current of the circuit to be metered, a secondarycoil on the electromagnet, in secondary transformer relation withrespect to the current coil, a resistance connected across saidsecondary coil, a voltage winding on the electromagnet, an energizingcircuit therefor, said current coil and voltage winding when energizedboth producing fluxes which tend to move the armature from detracted toattracted position against the bias of said spring, contacts for shortcircuiting the voltage winding onl when the armature is in detractedposition, a pointer, a second spring for advancing said pointer, anescapement device controlled by the operation of said armature forallowing a limited predetermined advance of said pointer for eachmovement of the armature to and from attracted position, such pointeradvancing operations progressively tensioning the first spring, andcontacts operated by said escapement during each pointer advancingoperation for momentarily short circuiting said resistance and openingthe energizing circuit of the voltage Winding to allow the return of thearmature to detracted position.

2. In a demand meter an electromagnet havingan E-shaped core with anarmature pivoted at the outer end of the middle leg on an axis at rightangles to such middle leg and extending between the outer legs, saidmiddle leg having flux carrying pole piece parts spaced from thearmature on opposite sides of it axis of rotation so that magneticattraction force between the armature and middle leg is equalized withrespect to the armature pivot in all armature positions whereby armaturepivot friction is not increased by reason of such attraction, the outerlegs having pole piece parts facing opposite sides of the armature sothat the attractive force at opposite ends of the armature producesrotation of the armature on its pivot in the same direction.

3. In a peak demand meter an alternating current electromagnet having anE-shaped core with a movable armature pivoted at the outer end of themiddle leg and extendin between the outer legs, means for biasing saidarmature to detracted position, a peak current coil on the riddle legenergized in response to current surges to be measured for overcomingsaid bias sufiiciently to start initial movement of the armature toattracted position, a voltage winding on the outer legs of the corewhich when energized completes the movement of the armature to attractedposition, contacts for short circuiting the voltage winding only whenthe armature is in detracted position, a secondary transformer windingalso on the middle leg of the core and a resistance connected in serieswith the secondary winding, said secondary transformer circuit havingsuch constants as to cause the initial armature attractive forceproduced by the flux of the peak current coil to be substantiallyindependent of the duration of the current surges therethrough.

4. A peak current demand meter comprising an electromagnet, a pivotedarmature therefor, movable between attracted and detracted positions, a

first spring for biasing said armature to detracted position, a currentcoil on the electromagnet energized in accordance with the variable loadcurrent to be metered, a secondary coil on the electromagnet intransformer relation with respect to the current coil used as a primary,a resistance connected across the secondary coil, a voltage winding onthe electromagnet, an energizing circuit therefor including a currentlimiting and tuning condenser, said current coil when sufficientlyenergized. serving to start and the voltage winding when energizedserving to complete movement of the armature from detracted to attractedposition against the bias of said spring, means for short circuiting thevoltage winding only when the armature is in detracted position, apointer, a second spring for advancing said pointer and increasing thetension of the first spring as the pointer is advanced to increase thebias on said armature, an escapement device controlled by the operationof the armature for allowin a limited predetermined advance of thepointer each time the armature is moved to and from attracted positionand contact operated by the escapement during each pointer advancingoperation thereof for short circuiting said resistance and opening theenergizing circuit of the voltage winding for a sufficient length oftime to allow the armature to return to detracted position.

5. In a peak demand meter, a pointer which is advanced in accordancewith peak current demand, aspring for advancing the same, an escapementfor controlling such advance, a pivoted escapement lever movable betweenstops for controlling the escapement, the lever having a complete cycleof movement for each advance of the escapement, an electromagnet formoving said lever in one direction to initiate an escapement advancingoperation, a second spring to move said lever in the opposite directionto complete the escapement advancing operation, said electromagnet havinan armature pivoted to move between detracted and attracted positionsand engageable with said lever when moved toward the attracted position,a third spring for biasing said armature to detracted position, thethird spring being tensioned by th first spring when the pointer isadvanced, a current coil on the electromagnet energized in response tothe current to be metered for overcoming the bias of said third springto start movement of the armature from its detracted position, a voltagewinding on the electromagnet which, when energized, completes themovement of said armature to attracted position, an energizing circuitfor the voltage winding, means for short circuitin said voltage windingonly when the armature i in detracted position, and means operated bythe escapement during an advancing operation for rendering saidelectromagnet ineffective to further attract said armature until thearmature has been returned to detracted postion, said lever having a lowinertia hinged part in operative relation with said second spring andarmature which allows for and assists the quick return of said armatureto detracted position.

6. A demand meter having an electromagnet provided with a pivotedarmature which is movable between detracted and attracted positions,winding means for said electromagnet for moving said armature fromdetracted to attracted position in response to predetermined currentvalues to be metered, a spring for biasing said armature to detractedposition, means for varying the tension of said spring to vary thecurrent value to which the electromagnet responds, a casing for saidmeter said meter bein pivotally supported within said casing on an axisof rotation above the center of gravity of the meter and parallel to andsubstantially coaxial with the axis of rotation of said armature todecrease the eiTect of vibration on the operation of the armature.

'7. A peak current demand meter comprising a pointer, a gear trainconnected thereto, a spring for advancing said gear train and pointer,an escapement for controlling the advance of the gear train, anelectromagnet provided with a movable armature for controlling theescapement, said electromagnet having two energizing windings, one ofwhich is energized in response to the current to be metered forproducing a minor initial attractive movement of the armature and theother of which is energized in response to such movement to complete themajor part of the attractive movement of said armature, whereby theforces required for the advance of the gear train and pointer and thecontrol of the escapement are merely controlled by the winding which isenergized in response to the current to be metered.

8. A peak current demand meter comprising a pointer, a gear trainconnected thereto, an escapement for said gear train, a spring foradvancing said gear train and pointer under the control of saidescapement, an electromagnet provided with a pivoted armature which whenmoved from detracted to attracted position and return, controls theoperation of said escapement, said armature having an initial minor freerange of movement from detracted position, a control Winding on saidelectromagnet energized in response to the current to be metered forproducing an initial free minor attractive movement of the armature, anenergizing winding on said electromagnet which is energized in responseto such initial free minor attractive movement of the armature forproducing a major and final attractive movement of the armature and thecontrol of said escapement, sprin means associated with the escapementtensioned by the major attractive armature movement to assist inreturning the armature to detracted position, means responsive to theresulting operation of said escapement and corresponding advance of saidgear train for interrupting the attractive force produced by both ofsaid windings to allow the armature to return to detracted position anda spring tensioned by the advance of said pointer for biasing thearmature to detracted position, the arrangement being such that thecontrol Winding merely controls the operation of said meter.

THEODORE A. HIGH.

